In general, as shown in FIG. 6, a fuel injection apparatus includes a field pump Fp for feeding a fuel contained in a fuel tank T to a high pressure pump Pp, the high pressure pump Pp for pressuring a fuel, a common rail R to which a high pressure fuel is supplied from the high pressure pump Pp, a pressure control valve V located between the common rail R and the fuel tank T, and a fuel injection nozzle I. The fuel pressure in the common rail R is controlled by the pressure control valve V so as not to exceed a predetermined level. The fuel in the common rail R is injected from the fuel injection nozzle I into a combustion chamber (not shown) of an engine.
A pressure control valve V of the type used in the fuel injection apparatus is disclosed in U.S. Pat. No. 5,558,068. This valve will be described with reference to FIG. 7.
The pressure control valve V includes a valve body fixedly inserted into an attachment hole Ha of a housing (attachment member) H of the common rail R. This valve body 1 comprises a seat member 2, and a plug member 3.
The seat member 2 is engaged fluid tight with a bottom portion side of the attachment hole Ha and abutted with a bottom surface of the attachment hole Ha through a gasket G. On the other hand, the plug member 3 is threadingly engaged with an upper end opening portion side of the attachment hole Ha. A lower end face of the plug member 3 is abutted against an upper end face of the seat member 2. Accordingly, when the plug member is tightened, the seat member 2 is urged against the bottom surface of the attachment hole Ha through the gasket G. By this, the seat member 2 and the plug member 3 are fixed to the housing H.
A vertical through-hole (guide hole) 2a is formed inside the seat member 2. This through-hole 2a is in communication with a fuel lead-in port P1 through a gap formed between an inner peripheral surface of the attachment hole Ha and an outer peripheral surface of the seat member 2. The fuel lead-in port P1 is connected to a fuel reservoir Ra inside the common rail R. A tapered valve seat 2c is formed on an upper end opening portion of the through-hole 2a.
A vertical through-hole 3a is formed inside the plug member 3. An upper end opening portion of this hole 3a is hermetically closed with a closure member 4. A lower end opening portion of the hole 3a is hermetically closed with the upper end face of the seat member 2. By this, A valve receiving chamber 5 is formed inside the hole 3a. This valve receiving chamber 5 is in communication with a fuel lead-out port P2 through a cross hole 3b and a gap formed between an inner peripheral surfaces of a cross hole 3b and the attachment hole Ha and an outer peripheral surface of the plug member 3. The fuel lead-out port P2 is connected to the fuel tank T.
A valve element 6 is vertically movably provided in the valve receiving chamber 5. This valve element 6 is formed with a valve portion 6a, a reduced diameter portion 6b, and a guide portion 6c in order from its upper end side towards its lower end side. The valve portion 6a is caused to sit on the valve seat 2c by a valve spring 7. The guide portion 6c is slidably engaged in the through-hole 2a. A damper chamber 8 filled with fuel is formed on a lower end portion of the through-hole 2a by the guide portion 6c and the bottom surface of the attachment hole Ha.
When the fuel pressure in the fuel reservoir Ra of the common rail R is equal to or less than a predetermined level in the pressure control valve V thus constructed, the valve element 6 is caused to sit on the valve seat 2c by the valve spring 7. Accordingly, no fuel in the common rail R returns to the fuel tank T. On the other hand, when the fuel pressure in the fuel reservoir Ra becomes higher than the prescribed level, the valve element 6 is lifted from the valve seat 2c against a biasing force of the valve spring 7. As a result, the fuel introduced into the attachment hole Ha from the fuel lead-in port P1 is returned from the fuel lead-out port P2 to the fuel tank T via the cross hole 2b, the through-hole 2a, the valve receiving chamber 5, and the cross hole 3b. By this, the fuel pressure in the fuel reservoir Ra is maintained equal to or less than the predetermined level.
When the valve element 6 makes a sitting movement and a lifting movement in the pressure control valve V, the guide portion 6c is guided by the through-hole 2a. Accordingly, the valve element 6 can smoothly move in a vertical direction. Moreover, when the valve element 6 moves, the fuel in the damper chamber 8 flows towards the cross hole 2b through a slide gap formed between the inner peripheral surface of the through-hole 2a and the outer peripheral surface of the guide portion 6c or the fuel in the cross hole 2b flows into the damper chamber 8. At that time, the slide gap acts as a sort of an orifice. Accordingly, the damper chamber 8 exhibits a damping function to prevent the valve element 6 from abruptly making a lifting movement and a sitting movement. By this, hunting of the valve element 6 is prevented.
Since the seat member 2 is urged against the bottom surface of the attachment hole Ha by the plug member 3 in the above-mentioned pressure control valve, the seat portion 2 is deformed and the valve seat 2c and the through-hole 2a are deformed. Deformation of the valve seat 2c degrades the hermetic closability between the valve portion 6a and the valve seat 2c. For this reason, there is such a fear that fuel leaks between the valve seat 2c and the valve portion 6a, and the fuel pressure in the common rail R cannot reach the predetermined level when the engine is rotating at a low speed.
When the through-hole 2a is deformed, the guide portion 6c becomes unable to move smoothly within the through-hole 2a and the smooth lifting and sitting movements of the valve element 6 with respect to the valve seat 2c are jeopardized. As a result, there is a fear that the pressure adjustment function to be exhibited by the pressure control valve V is adversely affected. Moreover, a desired damping effect to be exhibited by the damper chamber 8 cannot be obtained because when the through-hole 2a is deformed, the slide gap between through-hole 2a and the guide portion 6c greatly varies in largeness.